Franken, who faced enormous pressure from his own colleagues to step down, insisted he had done nothing to bring "dishonor" to the Senate since joining the body in 2009. He also expressed confidence that an ethics panel would have cleared him.

“I know in my heart that nothing I have done as a senator, nothing, has brought dishonor on this institution, and I am confident that the Ethics Committee would agree," he said from the Senate floor. "Nevertheless, today I am announcing that in the coming weeks I will be resigning as a member of the United States Senate.”

"I of all people am aware that there is some irony in the fact that I am leaving, while a man who has bragged on tape about his history of sexual assault sits in the Oval Office and a man who has repeatedly preyed on young girls campaigns for the Senate with the full support of his party," Franken said.

"But this decision is not about me. It's about the people of Minnesota.

“It's become clear that I can't pursue the Ethics Committee process and at the same time remain an effective senator for them,” he said.

Trump faced multiple accusations of sexual misconduct and harassment during his presidential run last year. Moore, the favorite to win Alabama's special election for the Senate on Tuesday, has been accused of having a sexual encounter decades ago with a 14-year-old when he was 32.

The decision caps off a chaotic 24 hours on Capitol Hill.

Democrats who previously had been comfortable allowing an ethics probe to proceed against Franken turned against him suddenly on Wednesday after a new accuser came forward.

Eight women have made accusations against Franken, a former “Saturday Night Live” writer and author seen as a possible 2020 presidential contender before controversy engulfed him.

A Democratic aide told The Hill that senators had been privately discussing how to handle Franken “for a while” and that the new accusation on Wednesday proved too much for them.

“This latest story certainly prompted continued conversations, and this morning members talked to each other about not waiting any longer to come out and call for him to resign,” the aide said.

Franken said in his Thursday speech that he was "shocked" and "upset" by the string of accusations that have surface against him, but he offered no new apology and in fact said he had not admitted to any wrongdoing in previous statements.

"In responding to their claims, I also wanted to be respectful of that broader conversation because all women deserve to be heard and their experiences taken seriously. ... [But] I also think it gave some people the false impression that I was admitting to doing things that, in fact, I haven't done," he said.

Franken didn’t specify when he will step down on, but his broad timeline outlined in his floor speech could line up with the Senate’s schedule to wrap up its work for the year in late December.

Under state law, Minnesota Gov. Mark Dayton (D) would appoint a candidate to serve until the 2018 elections, meaning the seat would likely stay in Democratic hands for at least the next 11 months.

It was reported on Thursday that Dayton would likely appoint Lt. Gov. Tina Smith to replace Franken.

“I expect to make and announce my decision in the next couple of days. I will have no further comments on this subject until that time,” he said in a statement.

Whoever wins the 2018 election would serve out the remainder of Franken’s term, which runs through 2020. An election would be held in 2020 for a full six-year term.

Meanwhile, former Sen. Norm Coleman, a Republican who Franken defeated in 2008 by a few hundred votes, declined to rule out a potential bid on Wednesday.

Republicans immediately appeared confident they would be able to pick up Franken's seat next year, as Democrats play defense in dozens of seats.

“The [National Republican Senatorial Committee] is confident Republicans will be able to win this soon-to-be vacant Senate seat come November, and look forward to expanding our Senate Majority,” Michael McAdams, a spokesman for the National Republican Senatorial Committee said shortly after Franken's speech.

Though the state hasn't gone Republican in a presidential campaign in decades, Trump narrowly lost the state by less than 2 percentage points last year.